A process of manufacturing semiconductor devices includes a liquid processing such as cleaning and etching, which are performed by supplying a processing liquid onto a substrate. In order to perform such a liquid processing, a liquid processing system provided with a plurality of liquid processing units is employed, as described in, for example, Japanese Patent Laid-Open Publication No. 2009-172459.
The liquid processing system as described in Japanese Patent Laid-Open Publication No. 2009-172459 includes a tank configured to store a processing liquid, a circulation line connected to the tank, and a pump configured to circulate the processing liquid stored in the tank to the circulation line. The circulation line is connected with a plurality of liquid processing units through branch lines, respectively, and each liquid processing unit performs a predetermined liquid processing on a substrate using the processing liquid that circulates the circulation line.
The processing liquid used for the liquid processing is adjusted by supplying a plurality of raw material liquids from independent raw material liquid supply lines, respectively, to the tank by a predetermined amount, and mixing the raw material liquids in the tank. When the processing liquid is adjusted by the mixing in the tank in this manner, the processing liquid may flow out from the tank before the raw material liquids are mixed sufficiently with each other in the tank. Therefore, the processing liquid may be supplied to the liquid units at an appropriate concentration.
Further, a liquid flow controller (LFC) is provided in each raw material liquid supply line, and each raw material liquid is supplied to the tank depending on a set flow rate and a supply time of each LFC. In a case where it is necessary to control the concentration of the processing liquid to a low concentration or within an allowable range, the supply amount may be insufficiently managed by the set flow rate and the supply time of each LFC.